This invention relates to systems and methods for tuning charged particle accelerators.
Charged particle accelerators may be used in a variety of applications. For example, a charged particle accelerator may be used to generate a high-energy electron beam in a radiation therapy device. The electron beam may be applied directly to one or more therapy sites on a patient, or it may be used to generate photon (e.g., X-ray) beams for treating a patient. As shown in FIG. 1, a conventional charged particle accelerator 10 for use in a medical radiotherapy device includes a series of accelerating cavities 12, 14, 16 that are aligned along a beam axis 18. A particle source 20 (e.g., an electron gun) directs charged particles into accelerating cavity 12. As the charged particles travel through the succession of accelerating cavities 12-16, the particles are focused and accelerated by an applied electromagnetic field (xe2x80x9cdriving signalxe2x80x9d) that is applied by an external source 22. Typically, the resulting accelerated particle beam 24 is directed to a magnetic energy filter 26 that bends beam 24 by approximately 270xc2x0. A filtered output beam 28 is directed through a window 30 to a target 32 that generates a photon beam 34. Other kinds of charged particle accelerators are well known in the art.
The operating efficiency of a charged particle accelerator is optimized when the resonant frequency of the accelerator matches the frequency of the applied driving signal. Although the physical characteristics of the accelerator needed to achieve the desired resonant frequency may be determined precisely, imperfections in the accelerator cavity structure may result from variations in the accelerator manufacturing process. These imperfections tend to detune the accelerator cavity structure. As a result, accelerators generally must be tuned before they can be used in an operable device.
Accelerators may be tuned manually by a tuning technician who physically deforms the structure of each accelerator cavity until the desired resonant frequency is achieved. The accelerator tuning process, however, involves a number of complex steps. For example, for each cavity of the accelerator (including each accelerating cavity and any off-axis coupling cavities), a tuning technician must prepare the accelerator for a measurement (e.g., configure the accelerator so that the cavity to be measured is isolated from the other cavities), measure one or more tuning parameters with a measurement instrument, and modify (e.g., deform) the physical structure of the cavity until a desired resonant frequency is achieved. In sum, in order to successfully and efficiently tune an accelerator, the tuning technician must prepare the accelerator for a plurality of different measurements, and must interpret and respond to the resulting plurality of measurement values.
The invention features a graphical user interface that guides a tuning technician through an accelerator tuning process and interfaces with a measurement instrument configured to measure characteristic parameters of the accelerator (e.g., a microwave or RF instrument, such as a network analyzer, a spectrum analyzer or a frequency counter) to enable the technician to make parameter measurements and interpret the results of those measurements more quickly and easily. In one aspect of the invention, a computer is programmed to generate the graphical user interface. In another aspect of the invention, a computer-readable medium carries instructions for generating the graphical user interface.
As used herein the term xe2x80x9ccomputerxe2x80x9d is intended to broadly refer to any programmable device that can respond to and execute a specific set of instructions (e.g., a program) in a well-defined manner. The term xe2x80x9cinterfacingxe2x80x9d is intended to broadly refer to the ability of two devices to communicate with each other.
In one embodiment, the graphical user interface is configured to display instructions for preparing the accelerator for a tuning parameter measurement by a measurement instrument. The graphical user interface may be configured to display the measurement preparation instructions pictorially or textually, or both. The graphical user interface preferably is configured to display tuning parameter values corresponding to measurements made before and after the accelerator has been tuned.
The graphical user interface may be configured to receive a user input and to generate a measurement command signal in response to the received user input. The graphical user interface also may be configured to display a tuning status indicator. The tuning status indicator may include a list of checkpoints in the accelerator tuning process.
The computer may be programmed to generate a second graphical user interface for displaying dynamic feedback information related to a measured tuning parameter (e.g., the resonant frequency of a cavity). The displayed dynamic feedback information preferably includes a representation of the difference between a measured tuning parameter value and a preselected tuning parameter value. The parameter value difference may be represented pictorially or numerically.
In one embodiment, the graphical user interface is configured to guide the user through a process of measuring one or more quality assurance parameter values, and the computer is programmed to store in memory the measured quality assurance parameter values and an associated accelerator identifier.
The invention also features an accelerator tuning method that includes the steps of guiding a user through an accelerator tuning process and interfacing with a measurement instrument configured to measure characteristic parameters of the accelerator.
Among the advantages of the invention are the following. The invention enables tuning technicians to tune accelerators in less time and with a greater accuracy than prior accelerator tuning approaches. In addition, the invention enables technicians to tune accelerators with significantly less training than prior approaches, reducing the considerable cost of developing and implementing elaborate accelerator tuning training programs.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.